Enriched rearing improved survival
Low survival of stocked fish has been associated with fitness declines of the captive reared fishes because of genetic domestication and unnatural rearing environments. The effects of broodstock origin (wild or captive) or rearing method (standard or enriched) on survival and migration of hatchery-reared Atlantic salmon smolts (Salmo salar) were investigated in the Tornionjoki River using radiotelemetry. Smolts that were reared with enriched methods had a twofold increase in survival (?38%) compared with smolts that had been reared in a standard hatchery environment (?19%). Nature-caught smolts had highest survival (?57%). Smolts from enriched rearing had a higher initial migration speed than fish from standard rearing. Initial migration speed during the first 3 km was positively correlated to survival probability after 290 km for hatchery fish. There was no clear effect of origin on survival or migration speed. The results of this study show that enriching the rearing environment with methods easily applicable to large-scale production promotes smolt survival and migration speed during river migration, which is imperative for stocking success.